Structural adhesives make heavy-duty advancements

Structural adhesives improve vehicle stiffness and acoustics. They can be applied manually or robotically. Typical applications include roof and floor bonding, as shown here.

Structural adhesives improve vehicle stiffness and acoustics. They can be applied manually or robotically. Typical applications include roof and floor bonding, as shown here.

Semi-structural adhesives provide both bonding and sealing properties and can adhere to wood, glass, polyurethane, sheet, and coated metal. They are paintable for a Class A finish. Typical applications include aluminum roof sheets, painted aluminum cant rails, composite or aluminum side panels, luggage compartments, and floors/carpets.

For the manufacture and design of commercial vehicles, structural adhesives can reduce the stress concentration around discontinuous joining methods such as spot welds or self-pierce rivets, resulting in mass-efficient design with improved durability performance.

Adhesives have long been used successfully in nonstructural and various applications for commercial vehicle manufacturing. Manufacturers of passenger cars are increasingly utilizing structural adhesives to provide added strength, durability, weight savings, and design benefits to vehicle body structure. And now the trend has extended to the commercial transportation market.

Global manufacturers of trucks, buses, rail cars, recreational vehicles, construction and agricultural equipment are now evaluating structural and semi-structural adhesives for applications such as body structure enhancement and side panel, roof, floor, and luggage bonding.

Structural adhesives are typically applied in the body shop during parts assembly. Various types of structural adhesives can be specified depending on application and manufacturing requirements including two-part and one-part moisture curing adhesives that do not require the use of e-coat paint and oven cure systems. E-coat paint processes are not prevalent in many heavy-truck manufacturing operations. Structural adhesives can also be used for aftermarket repair.

In many markets, commercial vehicle design changes slowly. However, structural adhesives will help accommodate design changes when needed. Because structural adhesives bond a variety of dissimilar materials, they can enable extensive design flexibility and freedom. The strength, versatility, and durability of structural adhesives will help designers plan and deliver next-generation vehicles that are lighter weight, more aerodynamic, safer, and more efficient to manufacture and have increased longevity.

Structural adhesives can bond dissimilar substrates, including aluminum, magnesium, and composites, which supports the trend toward lighter weight materials. They also provide increased static and dynamic stiffness to help improve vehicle quality, safety, and handling. And the lighter weight materials could enable trucks to pull heavier loads, increasing freight efficiency.

Compared to spot welds and mechanical fasteners, adhesives offer significant advantages. Corrosion and vibrational stress associated with spot welds and mechanical fasteners can be reduced or eliminated by forming continuous bond lines rather than single-point attachment. Structural adhesives enable weld reduction, which facilitates faster cycle times and reduced equipment cost. Structural adhesives also increase load-bearing capability, making them a good solution for reinforcing rails and other load-bearing members. Compared to mechanical fastening technology, adhesive applications significantly reduce the risks of repetitive task injury for the workforce.

The continuous bond line provided by structural and semi-structural adhesives offers corrosion protection and minimized water leakage as well as better strength and durability, contributing to longer vehicle life. The bond line also reduces metal fatigue/failure and improves overall vehicle aesthetics by reducing read-through.

As commercial vehicles and regulations continue to evolve, structural adhesives will keep pace. Industry experience will continue to inform suppliers such as Dow Automotive Systems so we can tailor solutions to commercial-vehicle platforms to provide benefits including weight savings, simplified assembly processes, and better design flexibility.

Tonja Sutton, North American Field Marketing Manager, Dow Automotive Systems, wrote this article for SAE Magazines.